Another good source that I didn't see mentioned is www.microfasteners.com. They have a good selection and are reasonably priced.
I like using 1-72 pan head screws for some things and find myself out of them and cannot remember what my source was. I know Woodland Scenics packages screws but they are pricey IMO. I am not fussy, stainless steel or brass would work fine. I need either 3/8" and 1/2" length. When I look online I am presented too many choices. I am curious if members have a suggested source. I want about 50 or so. Bill Welch